Efficacy of Pulsed 405-nm Light-Emitting Diodes for Antimicrobial Photodynamic Inactivation: Effects of Intensity, Frequency, and Duty Cycle

Abstract

Objective: This study investigates possible advantages in pulsed over continuous 405-nm light-emitting diode (LED) light for bacterial inactivation and energy efficiency. Background: Alternative nonantibiotic methods of disinfection and infection control have become of significant interest. Recent studies have demonstrated the application of systems using 405-nm LEDs for continuous disinfection of the clinical environment, and also for potential treatment of contaminated wounds. Methods: Liquid suspensions of 103 colony-forming units/mL populations of Staphylococcus aureus were subject to pulsed 405-nm light of different frequencies, duty cycles, and intensities and for different lengths of time. Results: Pulsed exposures with the same average irradiance of 16 mW/cm2 and varying duty cycle (25%, 50%, 75%) showed very similar performance compared with continuous exposures, with 95–98% reduction of S. aureus achieved for all duty cycles. The pulsing frequency was varied in intervals from 100 Hz to 10 kHz and appeared to have little effect on antimicrobial efficacy. However, when comparing pulsed with continuous exposure, an improvement in inactivation per unit optical energy was achieved, with results showing an increase of approximately 83% in optical efficiency. Conclusions: These results suggest that under pulsed conditions, a lower energy consumption and lower perceived brightness could be achieved, thus potentially providing improved operating conditions for medical/infection control applications without compromising antimicrobial efficacy.

Antimicrobial blue light inactivation of pathogenic microbes: State of the art

“…Gillespie et al compared the antimicrobial and operational efficacy of pulsed and continuously operated 405-nm LEDs (Gillespie et al, 2016). S. aureus suspensions containing 10 3 CFU/mL were exposed to continuous-wave 405 nm light for different lengths of time or pulsed 405-nm light of different frequencies, duty cycles, and intensities and for different lengths of time.…”

Immediate Placement of Ultrashort Implants in an Infected Site With Severe Loss of Soft Tissues and Bone Assisted by Lasers and Light‐Emitting Diode: Case Report With 3‐Year Follow‐Up

“…Indeed, as shown, 4 laser photoablation with the λ 810 nm diode laser can safely remove the infected soft periodontal tissues, yielding precise surgical incisions, no bleeding, and minimal edema and scarring, and resulting in better and faster healing than conventional surgery 11,12 . Irradiation with the λ 405 nm LED was used for its bactericidal efficacy, 5 whereas the λ 635 nm laser was used to induce photo‐biomodulation, being able to penetrate tissues without causing heating and cell injury and to stimulate various cellular processes 6,7 . Indeed, photobiomodulation is often used in medicine and dentistry to reduce pain, inflammation, fibrosis, and scarring while favoring hemostasis, healing, and repair/regeneration 10,11 .…”

“…2a) and irradiated for 5 minutes with λ 405 nm LED § (Fig. 2b) for reduction of bacteria and their proinflammatory byproducts, such as lipopolysaccharide 5 . A full‐thickness mucoperiosteal flap corresponding to teeth #10 to #12 was cut with the same laser equipped with a Ø 0.3 mm optical fiber (Fig.…”

“…2b) for reduction of bacteria and their proinflammatory byproducts, such as lipopolysaccharide. 5 A full-thickness mucoperiosteal flap corresponding to teeth #10 to #12 was cut with the same laser equipped with a Ø 0.3 mm optical fiber ( Fig. 2c) and lifted beyond the apical area of the teeth to expose the surgical field ( Fig.…”

Management of Severe Periodontal Abscesses Using a Laser and Light‐Emitting Diode Procedure Adjunctive to Scaling and Root Planing: A Case Series

“…This phenomenon prevents bleeding, yields a dry surgical field favoring access for SRP procedures in deep pockets, and reduces the odds for systemic bacterial spread during SRP manipulation. 3) The beneficial effects of laser photoablation are reinforced by the powerful antibacterial/antitoxin effect of λ 405‐nm violet‐blue LED phototherapy 12 and of multiple photodynamic sessions with methylene blue and λ 635‐diode laser 6,7,13 . As a matter of fact, all the abscesses treated with this combined therapeutic protocol underwent a particularly fast and satisfactory healing, resolving without complications and minimal gingival recession.…”